100% rated breakers vs their 80% standard rated counterparts

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kwired

Electron manager
Location
NE Nebraska
That, and the conductor sizing algorithm in general. It may seem like it is a question of just a few conductors, but it is a question that propagates across an entire project.

I was under the illusion that a continuous rated device is the same "gizmo" as the equivalent standard rated device that had been re-labelled with a different rating. And I wanted to understand if/how it really was any different.

My understanding has always been that it is all about terminal temperature - the 80% rated device needs larger conductor because the conductor is a heat sink for the breaker the 100% device though it may sink some heat into conductor is not as much as the standard breaker.
 

pv_n00b

Senior Member
Location
CA, USA
It's directly related to the heating of the CB due to continuous current. Remember that CBs react to heat as one of the indicators that it is time to trip. If the environment is warmer than they are rated for they will trip at a lower amperage and you will have false tripping. Not particularly dangerous but a pain to troubleshoot. So 100% rated CBs can take the heat of continuous current and still trip at the rated amperage. That's why the housing is part of the rated system, it's tested with the CB to make sure the heat is dissipated.
 
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